Vessel for removing radionuclides from a liquid

ABSTRACT

A vessel for removing radionuclides from a liquid. The vessel comprises a shielded housing comprising an outer shell and an inner shell disposed within the outer shell. The housing defines an ion exchange chamber between the inner and outer shells. The vessel also comprises an inlet fluidly coupled with the ion exchange chamber, the inlet being configured for fluid communication with a source of the liquid, and an outlet fluidly coupled with the ion exchange chamber, the outlet being configured for fluid communication with a destination of the liquid. The vessel further comprises a first fluid passage extending between an exterior of the vessel and the inner shell and a second fluid passage extending between the exterior of the vessel and the inner shell.

PRIORITY CLAIM

This application is a continuation of copending U.S. application Ser.No. 14/153,291, filed Jan. 13, 2014, which is based upon and claims thebenefit of U.S. provisional application Ser. No. 61/788,230, filed Mar.15, 2013. Both of the foregoing applications are incorporated fullyherein by reference.

RELATED APPLICATION

This application is also related to U.S. patent application Ser. No.14/153,277, filed on Jan. 13, 2014.

FIELD OF THE INVENTION

The present invention relates generally to treatment and disposal ofradionuclides in liquids.

BACKGROUND OF THE INVENTION

As is well known, radioactive materials are used extensively inindustrial, medical, agricultural, and environmental activities, amongothers. For example, radioactive waste is generated at nuclearfacilities, and there are a number of liquid processes and waste streamsat nuclear facilities that require treatment for removal of radioactivecontaminants. Management of this waste typically includes treatment,temporary storage, and transportation of the waste to a permanentdisposal site.

For example, the Savannah River Site (SRS) and the Hanford Site arenuclear reservations owned by the U.S. Department of Energy (DOE) andlocated in the states of South Carolina and Washington, respectively.The liquid waste operations contracts at these sites are respectivelyheld by Savannah River Remediation (SRR) and Washington River ProtectionSolutions (WRPS), which are teams of companies led by the URSCorporation. A major focus of these contracts is cleanup activitiesrelated to work done in the past at these sites.

In particular, large, highly toxic quantities of high-level radioactivewaste are located on the SRS and Hanford sites. At SRS, almost 40million gallons of this waste, containing hundreds of millions ofcuries, is found in the form of sludge, salt, and liquid. Predominantradionuclides are plutonium, strontium-90, and cesium-137. Strontium andcesium account for more than 95% of the radioactivity. Large amounts oftransuranic (TRU) waste are also stored on site. At Hanford, almost 60million gallons of similar waste exists.

The current plan to deal with this waste is to first pretreat the wastevia regenerable ion exchange at Hanford and liquid-liquid solventextraction and non-regenerable ion exchange at SRS to remove variousradionuclides. As is known, regenerable ion exchange and solventextraction are effective for transferring the radioactive content of alarge volume of liquid into a small volume of eluate and strip effluent,respectively, and non-regenerable ion exchange is effective fortransferring the radioactive content of a large volume of liquid into asmall volume of solid. Although ion exchange processes may beimplemented in a variety of ways, the most common uses of ion exchangemedia are as packed beds in vessels. More particularly, an ion exchangemedium is typically contained inside a stainless steel pressure vessel,with an engineered inlet, outlet, and flow distribution system to allowliquid to percolate uniformly through the bed of the medium at aspecified flow rate. Many types of ion exchange media are available forthis purpose, including inorganic and synthetic organic medias.

Secondary waste from the ion exchange or solvent extraction processes atHanford at SRS is eventually mixed with precipitated solids andimmobilized through a process called vitrification. Glass formingmaterials will be added to the waste at high temperature to form moltenglass. The molten material will then be poured into stainless steelcontainers, where the glass will harden as it cools. The waste willstill be radioactive, but no longer mobile (and thus not able to easilyspread into the environment). At SRS, a vitrification facility calledthe Defense Waste Processing Facility (DWPF) has been operating for thepast 15 years, with an operating expense of approximately one milliondollars a day. During this time period, the waste volume and sludgevolumes in the tanks have actually increased because of an insufficientcapacity to treat liquid waste. At Hanford, a vitrification facilitycalled the Waste Treatment Plant (WTP) has been under construction forthe past eleven years but is not expected to begin operations until atleast 2019 or beyond. Unfortunately, Hanford has multiple leaking tanksthat require processing prior to the operation of the vitrificationprocess.

SUMMARY

The present invention recognizes and addresses various considerations ofprior art constructions and methods. In this regard, embodiments of thepresent invention provide a vessel for removing radionuclides from aliquid. The vessel comprises a shielded housing defining an ion exchangechamber therein, the ion exchange chamber configured to receive ionexchange media in its interior between an interior top surface and aninterior bottom surface. An inlet diffuser is disposed in the ionexchange chamber proximate the bottom surface. An outlet collectionheader is disposed in the ion exchange chamber proximate the topsurface. A process inlet is in fluid communication with the inletdiffuser. A process outlet is in fluid communication with the outletcollection header.

Another aspect of the present invention provides an assembly configuredto be positioned near a storage tank containing radioactive liquid forremoving radionuclides from the liquid. The assembly comprises a filtervessel having at least one filter and further having a plurality of ionexchange vessels. The ion exchange vessels each comprise a shieldedhousing having an outer shell and an inner shell disposed within theouter shell, the housing defining an ion exchange chamber between theinner and outer shells. A process inlet and a process outlet are each influid communication with the ion exchange chamber. A first fluid passageextends between an exterior of the vessel and the inner shell. A secondfluid passage extends between the exterior of the vessel and the innershell.

A still further aspect of the present invention provides a vessel forremoving radionuclides from a liquid. The vessel comprises a shieldedhousing having an outer shell and an inner shell disposed within theouter shell, the housing defining an ion exchange chamber between theinner and outer shells. A base supporting the housing is also provided.A process inlet and a process outlet are each in fluid communicationwith the ion exchange chamber. A first fluid passage extends between anexterior of the vessel and the inner shell and a second fluid passageextends between the exterior of the vessel and the inner shell. Thevessel thereby permits convective air flow between the first fluidpassage, the inner shell, and the second fluid passage.

Those skilled in the art will appreciate the scope of the presentinvention and realize additional aspects thereof after reading thefollowing detailed description of preferred embodiments in associationwith the accompanying drawing figures.

BRIEF DESCRIPTION OF THE DRAWINGS

A full and enabling disclosure of the present invention, including thebest mode thereof directed to one of ordinary skill in the art, is setforth in the specification, which makes reference to the appendeddrawings, in which:

FIGS. 1A-1B are a schematic representation of an exemplary wastewatertreatment system at a nuclear facility comprising a near-tank filtrationand ion exchange assembly in accordance with an embodiment of thepresent invention.

FIG. 2 is an isometric view of a near-tank filtration and ion exchangeassembly in accordance with an embodiment of the present invention whichmay be used with the system of FIGS. 1A-1B.

FIG. 3 is a side elevation view of the near-tank filtration and ionexchange assembly of FIG. 2.

FIG. 4 is a top plan view of the near-tank filtration and ion exchangeassembly of FIG. 2.

FIG. 5 is an end elevation view of the near-tank filtration and ionexchange assembly of FIG. 2.

FIG. 6 is an isometric view of an exemplary ion exchange vessel that maybe used with the system of FIGS. 1A-1B, for example as part of thefiltration and ion exchange assembly of FIG. 2.

FIG. 7 is a side elevation view of the ion exchange vessel of FIG. 6.

FIG. 8 is a top plan view of the ion exchange vessel of FIG. 6.

FIG. 9 is a cross-sectional view of the ion exchange vessel of FIG. 6taken along line A-A of FIG. 8.

FIG. 10 is a cross-sectional detail view of the interface between theriser, upper plate, and ion exchange chamber of the ion exchange vesselof FIG. 6.

FIG. 11 is a cross-sectional detail view of the interface between theion exchange chamber, lower plate, and base of the ion exchange vesselof FIG. 6.

FIG. 12 is an isometric view of the ion exchange vessel of FIG. 6, withportions cut away.

FIG. 13 is a cross-sectional view of the ion exchange vessel of FIG. 6taken along line B-B of FIG. 8.

FIG. 14 is a cross-sectional view of the ion exchange vessel of FIG. 6taken along line C-C of FIG. 7.

FIG. 15 is a cross sectional view of the ion exchange vessel of FIG. 6taken along line D-D of FIG. 7.

Repeat use of reference characters in the present specification anddrawings is intended to represent same or analogous features or elementsof the invention.

DETAILED DESCRIPTION OF PREFERRED EMBODIMENTS

Reference will now be made in detail to presently preferred embodimentsof the invention, one or more examples of which are illustrated in theaccompanying drawings. Each example is provided by way of explanation ofthe invention, not limitation of the invention. In fact, it will beapparent to those skilled in the art that modifications and variationscan be made in the present invention without departing from the scope orspirit thereof. For instance, features illustrated or described as partof one embodiment may be used on another embodiment to yield a stillfurther embodiment. Thus, it is intended that the present inventioncovers such modifications and variations.

Various systems and techniques of liquid treatment for removal ofradioactive material in the liquid are shown and described in U.S. Pat.No. 6,387,274, entitled “System and Method for the Removal ofRadioactive Particulate from Liquid Waste”; U.S. Pat. No. 9,218,897,entitled “Wastewater Treatment and Radioactive Material DisposalContainer”; and International App. Pub. No. WO 2013/085644 (the '644publication), entitled “Fluid Treatment System.” The foregoing patentand patent applications are each incorporated herein by reference intheir entireties for all purposes.

Embodiments of the present invention provide a liquid treatment systemand a method for removing radionuclides from liquids. Some embodimentsof the present invention are particularly suitable for use in processingradioactive wastewater streams at nuclear facilities, and the belowdiscussion will describe preferred embodiments in that context. Forexample, embodiments of the present invention provide novel systems andmethods that can be used to address various wastewater issues, includingbut not limited to the leaking tank issue at Hanford described above.However, those of skill in the art will understand that the presentinvention is not so limited. In fact, it is contemplated thatembodiments of the present invention may be used with any liquidcontaining nuclear fission products and in industrial environments otherthan a nuclear facility.

As those familiar with the art will understand, there are many types ofbeaded and granular medias used for the selective removal ofcontaminants of such as radionuclides from aqueous liquids. As usedherein, the term “ion exchange” refers to any and all processes that mayoccur within the present invention, such as but not limited to ionexchange, adsorption, coprecipitation, etc. Therefore, the term “ionexchange” contemplates multiple removal mechanisms.

FIGS. 1A-1B are a schematic representation of a wastewater treatmentsystem 10 at a nuclear facility in accordance with an embodiment of thepresent invention. A volume of high-level nuclear waste, for examplecontaining one or more of radioactive strontium (Sr), actinides, andcesium (Cs), may be stored in a large storage tank 12. A given nuclearfacility may comprise many storage tanks 12, though only one such tankis shown. In one example, storage tank 12 may have a volume of over 1million gallons and store waste comprising supernate, salt cake, sludge,and solids. The supernate may comprise a liquid salt solution, which forexample may have high concentrations of sodium nitrate and sodiumnitrite salts. The sludge may contain precipitated solids and insolublewaste, and the solids may be in the form of crystallized salts(“saltcake”).

Certain inventive aspects of system 10 are described in more detailbelow. In general, however, system 10 operates to remove one or moreradionuclides (including but not limited to Sr, actinides, and Cs) fromthe supernate in storage tank 12, yielding a decontaminated saltsolution (DSS) 14. DSS 14 may then be sent to another facility (e.g.,via tanker trucks or pipeline) for further treatment 16 for finaldisposition. For example, DSS 14 may be immobilized in a grout, orcement, mixture and disposed in vaults. Those of skill in the art arefamiliar with other further treatments for DSS 14, such as transfer to alow level vitrifier. Finally, the sludge and solids in storage tank 12may be transferred to a separate storage tank for eventual high levelvitrification. The flow rate of liquid through system 10 may depend onthe salt concentration in the supernate in storage tank 12. For example,at a facility where the salt concentration is low, the flow rate may beapproximately 80-100 gallons/minute. Conversely, at a facility where thesalt concentration is higher, the flow rate may be approximately 20gallons/minute.

More particularly, in one embodiment, system 10 may first treat thewaste in storage tank 12 using a Monosodium Titanate (MST) strike.Although this treatment is not required in all embodiments, it may beused to adsorb Sr and actinides in the supernate in storage tank 12, aswill be appreciated by those of skill in the art. In this regard, atransfer pump 18 may pump MST from an MST storage tank 20 into storagetank 12. At least one submersible mixing pump 22 may be coupled withstorage tank 12 to ensure that the MST may sufficiently adsorb Sr andactinides in the supernate. In an alternative embodiment, a strike maybe performed external to tank 12 in a component or tank situated eitherupstream of the filtration vessel 30, in between the filtration vessel30 and the ion exchange vessels 38, 40, 42, or downstream of the ionexchange vessels 38, 40, 42.

Next, to process the supernate in storage tank 12, system 10 preferablycomprises a filtration and ion exchange assembly 24 in fluidcommunication with storage tank 12. As shown, for example, system 10 maycomprise a transfer pump 26 coupled with storage tank 12 that isoperable to pump the supernate from storage tank 12 to filtration andion exchange assembly 24 via suitable piping 28, which may besecondarily-contained and shielded. To avoid passing particulates orother solids into the ion exchange vessel(s), which may foul the ionexchange media, the liquid waste is preferably filtered upstreamthereof. Moreover, where an MST strike is used prior to filtration,filtration may further ensure that actinides are not present in thewaste stream that is fed into the ion exchange vessel(s).

Thus, filtration and ion exchange assembly 24 may preferably comprise aplurality of filters upstream of a plurality of ion exchange vessels. Inthe illustrated embodiment, filtration and ion exchange assembly 24comprises a filtration vessel 30 which includes three filters 32, 34,36. Further, filtration and ion exchange assembly 24 comprises three ionexchange vessels 38, 40, 42 in this embodiment. Ion exchange vessels 38,40, 42 may be in a lead-middle-lag configuration downstream offiltration vessel 30. Ion exchange vessels 38, 40, 42 are in fluidcommunication with filtration vessel 30 via piping 44, which may also besecondarily contained and shielded. Although three filters 32, 34, 36are shown in this embodiment, those of skill in the art will appreciatethat other embodiments may have fewer or more than three filters.Likewise, other embodiments may comprise two ion exchange vessels, forexample in a lead-lag configuration, one ion exchange vessel, or morethan three ion exchange vessels, depending on the requirements of aparticular liquid treatment system.

In a preferred embodiment, filters 32, 34, 36 may be rotary microfilters(RMFs) operating in parallel or in series. Those of skill in the art arefamiliar with RMFs suitable for this purpose, but in a preferredembodiment, the RMFs may be analogous to the RMFs described in U.S. Pat.No. 7,926,666, the disclosure of which is incorporated by referenceherein in its entirety for all purposes. Commercially available RMFs areoffered by Spintek Filtration of Los Alamitos, Calif. Additionally,aspects of RMFs are described in Christophe A. Serra & Mark R. Wiesner,A Comparison of Rotating and Stationary Membrane Disk Filters UsingComputational Fluid Dynamics, Journal of Membrane Science 165 (2000)19-29, incorporated herein by reference in its entirety for allpurposes. Other embodiments may of course use other suitable filtersknown to those of skill in the art.

Preferably, the RMF units and their associated piping are mounted infiltration vessel 30, which is preferably suitably shielded. The RMFunits may be mounted into the top of the filtration vessel 30 with arotating mechanical seal or similar sealing device that allowspressurized operation of the RMF. This configuration allows both thefiltration vessel 30 and the ion exchange vessels 38, 40, 42 to behandled and moved with the exact same hoist and mechanical rigging. Inone embodiment, each RMF unit may contain 25 flat, round 0.5 micronfilter element disks set on a hollow rotating shaft inside a stationarycylindrical housing. Supernate from storage tank 12 enters filtrationvessel 30, where it is then fed into each RMF unit. The supernate isdistributed across each RMF element surface and is forced through eachfilter element. The permeate (aka filtrate) which results from themicrofiltration is a filtered salt solution (FSS). The FSS may becollected in the hollow shaft of each RMF and discharged to piping 44,where it is transferred to ion exchange vessel 38.

The retentate stream (sometimes known as a concentrate or reject stream)output from the RMF(s) may be continuously returned to storage tank 12.In particular, in each RMF, stationary disks oppose the rotating elementdisks and thus act to prohibit fluid rotation. Rather than depositing onthe filter elements, solids may be carried into a return piping 46 viacentrifugal force. Return piping 46, like piping 28 and 44 above, maypreferably be secondarily contained and shielded. It will thus beappreciated that a back pulse system is not required, though it may beprovided in some embodiments. (Further, some embodiments of filters 32,34, 36 may comprise a connection by which acid or other chemicals may beadded for cleaning and dissolving debris from the filter element.)Piping 46 then carries the retentate stream back to storage tank 12.

Although FIGS. 1A-1B illustrate filters 32, 34, 36 operating inparallel, it will be appreciated that filters 32, 34, 36 may also beoperated in series, as noted above. In fact, in some installations aseries operation may provide better performance than parallel operationdue to high cross-flow “flushing” velocities. The feed flow to filter 32may have somewhat similar characteristics to the rententate streamoutput from filter 32 because only a small portion of the process streammay be removed as filtrate, and thus configuring the retentate streamoutput from filter 32 to flow into a second or third filter (such asfilters 34 or 36) is not a problem.

FSS leaving filtration vessel 30 may then pass through a turbidityanalyzer 48. Turbidity analyzer 48 may analyze the turbidity of the FSSto ensure that filters 32, 34, 36 are operating properly. Should theturbidity measurement fail to be acceptable, then the treatment system10 may be shut-down prior to fouling of the ion exchange media.

Assuming the turbidity measurement is acceptable, the FSS passes viapiping 44 to ion exchange vessels 38, 40, and 42, in sequence, forremoval of radionuclides. In one embodiment, ion exchange vessels 38,40, 42 may be used to remove Cs from the FSS, though they may removeother radionuclides in addition or in alternative to Cs in otherembodiments. In the illustrated embodiment, ion exchange vessels 38, 40,and 42 may each preferably be loaded with suitable ion exchange mediafor removing Cs. In preferred embodiments, the ion exchange media may beCrystalline Silicotitanate (CST) media. Examples of commerciallyavailable CST media are IONSIV® IE-911, offered by UOP LLC of DesPlaines, Ill., and HS-726, offered by Hitachi GE Nuclear Energy, Ltd. ofHitachi City, Japan. As those of skill in the art will appreciate, CSTmedia has a high affinity for Cs (and may also be used to remove Sr),but it is a non-regenerable sorbent that can only be loaded once. Thus,once the CST media in a given ion exchange vessel is spent (which mayfor example be after approximately weeks or months of use, depending onthe physical, chemical, and radiological characteristics of the FSS),the ion exchange vessel may preferably be removed from service andplaced in storage pending further processing. During storage, the loadedCST media generates heat, and thus the stored ion exchange vessels mayneed to be cooled. One example of a technique for passively cooling thestored ion exchange vessels is provided in the above-referenced '644publication. In other embodiments, loaded ion exchange media may besluiced from the appropriate ion exchange vessel to a separate storagetank for further processing and/or storage.

Importantly, and as discussed in more detail below, ion exchange vessels38, 40, and 42 are preferably operated in up-flow, rather than indown-flow, which is used in the prior art. Thus, FSS may first flow frompiping 44 into lead ion exchange vessel 38, where it flows upwardthrough the ion exchange media. The FSS stream may then exit ionexchange vessel 38 via piping 52 and enter middle ion exchange vessel40. After flowing upward through the ion exchange media therein, the FSSstream may exit ion exchange vessel 40 via piping 54 and enter lag ionexchange vessel 42. Finally, the FSS stream may exit ion exchange vessel42 via piping 56. Piping 52, 54, 56 may preferably be secondarilycontained and shielded.

As noted above, the output from ion exchange vessel 42 is DSS 14. DSS 14may pass along piping 56 and encounter a radiation detector 58.Radiation detector 58, which in one embodiment may be a scintillationdetector using sodium iodide activated with thallium (or anothersuitable scintillation detector), may analyze DSS 14 for the presence ofionizing radiation. Thus, radiation detector 58 may serve as a grossindicator of whether the ion exchange process is suitably removing thetargeted radionuclide from the FSS stream. Radiation detector 58 maythus also provide information regarding whether the ion exchange mediais spent, thus alerting the operator to shut-down the treatment system10 for ion exchange vessel 38, 40, 42 replacement or a similar remedialaction.

Assuming the targeted radionuclide (e.g., Cs and/or Sr) has beensuitably removed, DSS 14 then passes into two sample tanks 60, 62. DSS14 is circulated (mixed) and stored in sample tanks 60, 62 so thatpersonnel may sample DSS 14 and ensure that it meets applicable wasteacceptance criteria for any further treatment 16. System 10 may furthercomprise two pumps 64, 66 in a parallel configuration. When it isdetermined that the waste acceptance criteria have been satisfied, pumps64, 66 are operable to pump DSS 14 to the appropriate further treatment16 such as via suitable secondarily-contained, shielded piping 68.Although only one pump 64 or 66 may be required, two pumps 64 and 66provides redundancy. In use, only one of pumps 64 and 66 may operateuntil worn-out, in which case the other could be readily implemented.Pumps 64, 66 are preferably in fluid communication with tanks 60, 62 viapiping 70, which may also be secondarily-contained and shielded.

Typically, only one of sample tanks 60 or 62 may receive DSS 14 fromfiltration and ion exchange assembly 24 at a time, which allows theother of tanks 60 or 62 to be sampled. Notably, system 10 preferablycomprises a bypass loop to facilitate mixing of the DSS 14 in the tank60 or 62 that is being sampled. In particular, sample tanks 60, 62preferably comprise mixing eductors 72, 74 disposed therein to mix theDSS 14 and ensure a homogenous sample. Via piping 76, mixing eductors72, 74 are preferably in fluid communication with piping 70 downstreamof pumps 64, 66. Thus, for example, when tank 60 is being sampled, tank62 may be receiving DSS 14 from filtration and ion exchange assembly 24.System 10 may cause the pump 64 or 66 that is in operation to pump DSS14 out of tank 60. System 10 may then cause the DSS 14 leaving the pumpto bypass further treatment 16 and instead pass from piping 70 intopiping 76, ultimately returning to mixing eductor 72, which mixes DSS 14in tank 60. Assuming the sample meets the applicable waste acceptancecriteria, system 10 may then cause the pump to pump DSS 14 from tank 60to further treatment 16. DSS 14 stored in tank 62 may then be mixed andsampled in a similar fashion, and tank 60 may then receive DSS 14 fromfiltration and ion exchange assembly 24.

Those of skill in the art will appreciate that large amounts of heat maybe generated during operation of system 10. When system 10 is operating,the liquid stream flowing through system 10 cools the variouscomponents. However, when system 10 is shutdown for any reason, theliquid stream may not be flowing. Thus, system 10 may comprise a standbycooling loop 78 which may extend at least between piping 56 (downstreamof ion exchange vessels 38, 40, and 42) and piping 44 (upstream of ionexchange vessels 38, 40, and 42). As shown, cooling loop 78 may comprisea heat exchanger 80 which may facilitate heat transfer from the heatedliquid waste stream. A pump 81 may be provided along cooling loop 78upstream of heat exchanger 80 to pump the liquid stream therealong.Additionally, as indicated by broken line 82, in other embodimentscooling loop 78 may extend to piping 28 upstream of filtration vessel30.

Further, those of skill in the art are familiar with suitablemaintenance systems for system 10. In one nonlimiting example, inhibitedwater, such as water mixed with sodium hydroxide, may be pumped from atank 84 and used to clean system 10 components. Inhibited water is usedto maintain needed or desired pH levels in certain system components, asthose of skill in the art will appreciate. Tank 84 may be in fluidcommunication with piping 28 via piping 86. A pump 88 disposed alongpiping 86 may be used to pump the inhibited water from tank 84 intopiping 28 and the other components in system 10. Thus, when system 10 isnot in use, the inhibited water may be used to flush filtration and ionexchange assembly 24 for maintenance or to prevent corrosion.

In addition, system 10 may be configured to receive compressed air froma compressed air source 90. In particular, via piping 92, compressed airsource 90 may be in fluid communication with piping 10 (and thus, theother system components). Accordingly, compressed air source 90 mayforce air throughout system 10 to remove water from components of system10, for example prior to disconnecting a component for repair orservice.

FIGS. 2-5 illustrate additional details regarding embodiments offiltration and ion exchange assembly 24. By way of background,wastewater treatment systems at nuclear facilities are often somewhatdecentralized. For example, the storage tank containing wastewater to beprocessed may be separated from other system components, such asfilters, ion exchange components, or other storage tanks, by miles ofpiping. As will be appreciated, this is both expensive and inefficient.Further, as described above, although CST media is a particularlyeffective media for removing Cs and/or Sr from liquid feed streams,significant amounts of decay heat can be generated from loaded (spent)media. Thus, although large ion exchange vessels using CST media havebeen proposed for treatment of salt wastes at nuclear facilities, theyhave not been adopted due to containment, heat dissipation, andshielding requirements.

More recently, however, in an effort to avoid these containment, heatdissipation, and shielding requirements, it has been proposed to installa smaller ion exchange vessel in an “in-tank” configuration. Moreparticularly, in this configuration, system components, including pumps,filters, and ion exchange columns, are installed inside a riser disposedon top of the storage tank. Because the tank also includes secondarycontainment and shielding, it is not necessary to build additionalshielded facilities. The system components extend into the storage tankto process the liquid waste located therein.

However, there are a number of drawbacks to such an in-tankconfiguration. First, installing a column into the tank is challengingdue to the close tolerances and hazardous environment. In particular,the treatment column must fit precisely within a riser located on a tankthat may have been constructed several decades prior. Even thoughdrawings may exist, achieving a perfect fit-up between the “in-tank” ionexchange column and the riser will be challenging. This may beespecially true because the riser is in a hazardous environment wherework activities are complicated due to personal protective equipmentrequirements. Second, due to the weight and dimensional limitations, itis not practical to add shielding to an in-tank type column. Therefore,the in-tank column cannot be simply removed from service and placed intostorage (like embodiments of the present invention). This furthercomplicates operations because the loaded media must be transferred fromthe column through interconnecting piping to a grinding component thatreduces the ion exchange media size to approximately 30-micrometers orless. This may allow the ground CST to mix with ambient tank sludgewithout separating. Third, there is minimal air flow inside the highlevel waste tanks. Therefore, the in-tank column must be actively cooledat all times. Fourth, the waste tank must have substantial structuralstrength and integrity to hold the weight of the in-tank column and itsancillary components, such as an RMF prefilter and media grinder.Accordingly, only the Type III tanks at SRS have been qualified tosupport the in-tank components. It is expected that most olderfacilities will not want to add this amount of weight and increasedstresses on tanks that may already be leaking.

In contrast, and as described in more detail below, the configuration ofthe components of filtration and ion exchange assembly 24 preferablyallow the assembly to be positioned in a simple “near-tank” facility. Inother words, components of filtration and ion exchange assembly 24 neednot be and are not installed “in-tank” or in one or more separateshielded structures or facilities remote from the storage tank. Thus,extensive piping between a storage tank and other components is nolonger required. Of course, the proximity of embodiments of filtrationand ion exchange assembly 24 to a given waste tank may be dictated bythe requirements at a given facility. To take two nonlimiting examples,embodiments of filtration and ion exchange assembly 24 may be locatedwithin 500 feet of waste tanks at the Hanford facility, and embodimentsof filtration and ion exchange assembly 24 may be located up to 5000feet from the waste tanks at the Fukushima facility in Japan. In anyevent, because they are configured to be positioned adjacent to or inclose proximity to a liquid storage tank, embodiments of the filtrationand ion exchange assembly 24 may be portable, in that they may bedisassembled and moved from one tank to the next as a particular job iscompleted.

As shown in FIGS. 2-5, in one embodiment, filtration and ion exchangeassembly 24 may comprise a gangway 100. Gangway 100 may provide atechnician or other personnel access to filtration vessel 30 and ionexchange vessels 38, 40, 42. In this regard, gangway 100 preferablycomprises an elevated platform 102 and a support structure, orunderbody, 104 which supports platform 102. Gangway 100 may preferablybe of a lightweight metal construction, for example welded steel oraluminum. Notably, piping (e.g., piping 28, 44, 52, 54, 58) and othercomponents associated with filtration vessel 30 and ion exchange vessels38, 40, 42 may be disposed beneath platform 102 in underbody 100. Thus,underbody 100 may provide an area where traditionally more spread outcomponents may be located in a compact footprint that is also readilyaccessible, which facilitates near-tank placement.

Preferably, filtration vessel 30 and ion exchange vessels 38, 40, 42 maybe equally spaced alongside of and parallel with platform 102. Further,the vessels are preferably spaced close enough to gangway 100 to provideready access thereto by an operator standing on platform 102. In thisregard, gangway 100 may also comprise guardrails 106 surroundingplatform 102, which may be accessible by stairs 108 and/or a ladder 110.As shown, in one embodiment, the construction of filtration vessel 30 ispreferably in several respects analogous to that of ion exchange vessels38, 40, 42, aspects of which are described in greater detail below,though this is not required.

FIGS. 6-15 illustrate an ion exchange vessel 150 constructed inaccordance with an embodiment of the present invention. Ion exchangevessel 150 may be used with system 10 as a component of filtration andion exchange assembly 24. Thus, ion exchange vessels 38, 40, and 42 maypreferably be analogous to ion exchange vessel 150 in some embodiments.In other embodiments, however, ion exchange vessel 150 may be used as astandalone unit or as part of another liquid treatment system. In apreferred embodiment, ion exchange vessel 150 may be constructed to meetapplicable requirements regarding the construction of pressure vessels,such as the requirements defined in the American Society of MechanicalEngineers Boiler and Pressure Vessel Code, Section VIII (incorporated byreference herein in its entirety for all purposes).

Ion exchange vessel 150 may preferably also serve as a storage modulefor spent ion exchange media. For example, vessel 150 may be broughtinto a nuclear facility and connected to plant equipment, where watermay flow through the vessel until the media reaches its maximumradiological capacity (e.g., maximum Cs & Sr loading) or is exhausted(DF≈1). At this point, water may be blown from the vessel, connectionsmay be secured, and the vessel may be transported to an interim spentstorage facility. There, the vessel may be stored for a long period oftime (for example many years or up to hundreds of years) to allowradiolytic decay of the radionuclides, after which time the spent mediamay be removed and disposed of as low-level radioactive waste.

Referring now to the figures, ion exchange vessel 150 may comprise anouter shell 152 extending between middle and lower plates 154, 156,respectively. Outer shell 152 and plates 154, 156 may thereby define anion exchange chamber 153. In operation of ion exchange vessel 150, ionexchange chamber 153 may be filled with any ion exchange media that isneeded or desired for a particular liquid treatment process. In theexample of system 10 discussed above, ion exchange chamber 153 may befilled with CST type media. In this regard, FIGS. 9 and 12-14 illustrateion exchange vessel filled with ion exchange media to a height 209. Inany event, in a preferred embodiment, outer shell 152 may be cylindricalin shape and formed of an austenitic or duplex stainless steel (or asimilar corrosion-resistant alloy, such as Alloy 20, Hastelloy, etc.),though this is not required. Plates 154, 156 may likewise be formed ofstainless steel and be annular in shape, having centrally disposedapertures 155, 157 respectively defined therein. In one example, plates154, 156 may be approximately 3 in. thick and outer shell 152 may beapproximately 0.5 in. thick. The outer diameter of middle and lowerplates 154, 156 may preferably be substantially equal to the outerdiameter of outer shell 152.

Next, ion exchange vessel 150 may comprise a riser 158 which rests onmiddle plate 154 and a base 160 on which lower plate 156 rests. Riser158, which may preferably be formed of stainless steel, may also have anouter diameter that is substantially equal to the outer diameter ofouter shell 152 and plates 154, 156. As described in more detail below,base 160, which in one embodiment may comprise a plurality of stackedplates, may preferably have a somewhat larger outer diameter than thatof outer shell 152 and plates 154, 156. Ion exchange vessel 150 mayfurther be provided with a lifting trunnion 161 which, in theillustrated embodiment, may be integrally coupled with riser 158. Itwill be appreciated that lifting trunnion 161 may facilitate handlingand transport of ion exchange vessel 150.

Within riser 158 may be an upper plate 162 which is fixed above middleplate 154 such that riser 158, upper plate 162, and middle plate 154define an upper chamber 164. Upper plate 162 may preferably define anaperture 166 therein. Aperture 166, which in one embodiment may berectangular in shape, preferably has a centerline that is collinear witha diameter of upper plate 162 and is disposed over aperture 155 inmiddle plate 154. Accordingly, as discussed in more detail below, upperchamber 164 is not fully enclosed, but allows air to flow betweenaperture 155 and aperture 166. In this regard, a plate cover 168 may besecured over aperture 166 and a plate cover 170 may be secured overaperture 155. Upper plate 162 may also be formed of stainless steel and,in one embodiment, may be approximately 0.5 in. thick. Additionally, inone embodiment, plate covers 168 and 170 may be formed of 18 meshstainless steel.

Upper plate 162 may further define a pair of laterally-opposed apertures172, 174 spaced on either side of aperture 166, and middle plate 154 mayfurther define a pair of laterally-opposed apertures 176, 178 which arealigned with apertures 172, 174. Extending between aperture 172 andaperture 176 and between aperture 174 and aperture 178 may be tubing180, 182, respectively. Thereby, tubing 180 and tubing 182 may eachdefine a port 184, 186 through which a technician or other personnel mayinspect ion exchange chamber 153. Further, ports 184, 186 provide ameans for removing spent ion exchange media, for example for furtherprocessing (e.g., vitrification), storage, or disposal. Ports 184, 186may be closed by removable plugs or covers 188, 190. Plugs 188, 190,which may preferably be formed of stainless steel, may be secured overapertures 172, 174 in upper plate 162 with bolts or other suitablefasteners.

As noted above, ion exchange vessel 150 may preferably be configured tooperate in up-flow, rather than in down-flow as in the prior art. Inthis regard, ion exchange vessel 150 may comprise a process inlet 192disposed in riser 158 above upper plate 162. In one embodiment, processinlet 192 may comprise a 3 in. Drylok quick disconnect valve, flange, orsimilar connection point. Ion exchange vessel 150 may further comprisean inner shell 194 which preferably extends between lower plate 156 andmiddle plate 154 and may preferably have an inner diameter that issubstantially equal to that of apertures 155, 157. Preferably, innershell 194 may be formed of stainless steel (or another suitablecorrosion-resistant material as described above), and in one example itmay be approximately 0.5 in. thick. An inlet spool 196 may extend fromprocess inlet 192 through upper chamber 164 and down through inner shell194, where it may exit inner shell 194 into chamber 153 and terminate inan inlet diffuser 198. Thus, inner shell 194 may separate a portion ofinlet spool 196 from ion exchange chamber 153. Inlet diffuser 198, whichas shown may be annular in shape and concentric with inner shell 194,preferably comprises a plurality of downward-facing inlet screens 200.As will be appreciated by those of skill in the art, inlet screens 200may be cylindrical in shape and define a plurality of holes throughwhich liquid may enter ion exchange vessel 150. Inlet screens 200 arepreferably equally spaced about diffuser 198 to facilitate an evendistribution of liquid entering ion exchange vessel 150 in ion exchangechamber 153.

Ion exchange vessel 150 may further comprise a process outlet 202disposed in riser 158 above upper plate 162. In one embodiment, processoutlet 202 may comprise a 3 in. Drylok quick disconnect valve, flange,or similar connection point. An outlet spool 204 may extend from processoutlet 202 through upper chamber 164 and down through inner shell 194,where it may exit inner shell 194 into chamber 153 and terminate in anoutlet collection header 206. Thus, inner shell 194 may also separate aportion of outlet spool 204 from ion exchange chamber 153. Outletcollection header 206, which as shown may be annular in shape andconcentric with inner shell 194, may preferably be located proximatemiddle plate 154. Outlet collection header 206 preferably comprises aplurality of upward-facing outlet screens 208. Outlet screens 208 maypreferably be analogous to inlet screens 200, described above. Thus,outlet screens 208 are preferably equally spaced about header 206 tofacilitate collection of liquid exiting ion exchange chamber 153. Inthis regard, outlet screens 208 may preferably extend at least partiallyabove the height 209 of the ion exchange media in ion exchange chamber153.

In a preferred embodiment, process inlet and outlet 192, 202, inlet andoutlet spools 196, 204, and inlet diffuser and outlet collection headers198, 206 may all be formed of stainless steel. Moreover, in otherembodiments, process inlet and outlet 192, 202 need not be disposed inriser 158. For example, process inlet 192 could be located on theexterior of ion exchange vessel 150, such as at base 160.

A vent 210 may also be disposed in riser 158 above upper plate 162. Inone embodiment, vent 210 may comprise a 1 in. Drylok quick disconnectvalve, flange, or similar connection point. A vent spool 212 may extendfrom vent 210 through upper chamber 164. Vent spool 212 may also passthrough a corresponding aperture defined in upper plate 162 andterminate at ion exchange chamber 153. Preferably, vent spool 212 may beformed of stainless steel.

As shown, inlet diffuser 198 may preferably be located near the bottomof ion exchange chamber 153 such that inlet screens 200 are locatedproximate lower plate 156. Thus, liquid entering ion exchange vessel 150will enter at the bottom of ion exchange chamber 153, rather than at thetop as in the prior art, and flow upward through the ion exchange medialocated therein. After the liquid passes through the ion exchange mediaand reaches the top of ion exchange chamber 153, the liquid may becollected via outlet screens 208 associated with outlet collectionheader 206. The liquid may then flow upwards through outlet spool 204and exit ion exchange vessel 150 via process outlet 202.

Configuring ion exchange vessel 150 for up-flow operation has severalnotable advantages. For example, during operation, emission of radiationmay cause radiolytic decomposition of water and otherhydrogen-containing compounds that produces hydrogen gases. In prior artion exchange vessels operated in down-flow, at least some of these gasescould be trapped in the ion exchange chamber, which could lead to anexplosive environment within the ion exchange media or uneven flowdistribution that could lead to inefficient use of the media. Inembodiments of the ion exchange vessel of the present invention,however, up-flow operation passively purges these gases from the ionexchange chamber during regular operation. In particular, the gases arepassed into the effluent through outlet screens 208 associated withoutlet collection header 206. The gases then travel with the liquid,eventually ending at a storage tank (e.g., sample tanks 60, 62) that isappropriately vented through an engineered gas ventilation system. Inone example, a volume of up to 10 liters of gas/hour may be purged fromion exchange vessel 150. In one embodiment, vent 210 may be connected toa pressure air-release valve that automatically releases accumulatedgases to a facility's ventilation system.

Further, by operating ion exchange vessel 150 in up-flow, lower pressurecomponents may be used in the liquid treatment system. Moreparticularly, during use of prior art, down-flow systems, the incomingliquid flowing downward would cause the ion exchange media to compact.The compacted ion exchange media would create a high differentialpressure across the ion exchange vessel, thus requiring use of morepowerful pumps and other higher pressure components. In contrast,upward-flowing liquid does not cause compaction of ion exchange media,and thus the differential pressure across ion exchange vessel 150 may bequite lower than in the prior art.

Yet another advantage of up-flow operation relates to the radiationshielding on ion exchange vessel 150. As noted above, CST media has atremendous capacity and high affinity for Cs and Sr. As is known,however, this tends to cause Cs removed utilizing CST media to be moreconcentrated in the region first encountered by the Cs-containing liquidwhich enters the ion exchange chamber. In other words, in a down-flowion exchange vessel, the Cs would be concentrated in the upper portionof the ion exchange chamber because the liquid entering would flow fromtop to bottom. Notably, though, a greater concentration of radionuclidesin one area of the vessel may require greater shielding at thatlocation. However, including additional shielding (which may be formedof lead) at the upper portion of the ion exchange chamber may cause anion exchange vessel to have a high center of gravity and be somewhat“top heavy.” Having a higher center of gravity is undesirable forseveral reasons, including that it reduces the stability of the vesselduring seismic events (e.g., earthquakes) and that it increases thedifficulty of transporting the vessel.

In accordance with embodiments of the present invention, however, byoperating ion exchange vessel 150 in up-flow, removed radionuclides willtend to concentrate at the lower portion of ion exchange chamber 153.Thus, a lower portion of ion exchange vessel 150 may have shielding ofgreater thickness than the upper portion of ion exchange vessel 150. Forat least this reason, ion exchange vessel 150 may have a lower center ofgravity and be both more stable during seismic events and easier totransport. In addition, vessel 150 may be contact-handled from the top,and because upflow operation causes the highest radiation dose rates tobe nearer the bottom of vessel 150, it may also lower personnel orworker radiation exposure.

In this regard, ion exchange vessel 150 may preferably comprise uppershielding 214 and lower shielding 216. Preferably, shielding 214, 216 isformed of lead, though those of skill in the art are familiar with othersuitable shielding materials. As shown in the figures, upper shielding214 may be thinner than lower shielding 216. In one embodiment, uppershielding 214 may have an outer diameter approximately 3 in. less thanthat of lower shielding 216, making lower shielding 216 approximately1.5 in. thicker on all sides. Lower shielding 216 preferably extendsupward enough to adequately shield against concentrated radionuclides inthe inlet mass transfer zones. In one embodiment, for example, lowershielding 216 may extend upward approximately 56.5 in. from base 160,whereas upper shielding 214, which may rest on lower shielding 216, mayextend upward approximately 53.4 in. from lower shielding 216 and thusalso cover some portion of upper chamber 164.

Notably, in a preferred embodiment, shielding 214 and shielding 216 mayeach be formed by wrapping a plurality of lead sheets around theexterior surface of outer shell 152 to the desired thickness. In oneexample, lead sheets having a thickness of 3/16 in. and a length of 9ft. may be welded to each other (and, if necessary, to shell 152) toform the lead shielding. Importantly, wrapping the lead to form theshielding in this manner has several advantages. First, formingshielding 214, 216 by wrapping lead sheets makes it easier to achieve adifferential shielding thickness along the length of ion exchange vessel150. Moreover, as noted above, after the ion exchange media in vessel150 is spent, vessel 150 may be stored for a sufficient period of timeto allow radiolytic decay. By forming shielding 214, 216 of wrapped leadsheets, shielding 214, 216 may be more readily removed than prior artshielding when sufficient radiolytic decay has occurred. The lead maythen be separately dispositioned as non-radioactive material. Further,in one embodiment, forming the shielding in this manner may reduce thepresence of ionizing radiation by a factor of 1 million, which issignificantly greater than shielding on prior art ion exchange vessels.Nonetheless, it is contemplated that shielding 214 and 216 may be formedby other methods in other embodiments, such as by pouring lead orfilling a cavity with lead shot, etc.

In one embodiment, a “skin,” or casing, formed of carbon steel may besecured over shielding 214, 216. (The casing is not shown in FIG. 12.)In particular, an upper lateral casing 218 may comprise a pair of steelsheets which have been plate-rolled into a semicircular shape andoppositely positioned over upper shielding 214. The longitudinal edgesof each sheet may be turned outward such that when the sheets aresecured over upper shielding 214, they form diametrically-opposed lips220, 222. Likewise, a lower lateral casing 224 having lips 226, 228 maybe formed in a similar fashion and secured over lower shielding 216.Lips 220, 222, 226, 228 may be secured to one another using suitablefasteners, such as bolts or the like.

In addition, an upper shelf casing 230 may be secured over the flat,shelf-like portion of upper shielding 214 which extends between riser158 and upper lateral casing 218. Likewise, a lower shelf casing 232 maybe secured over the flat, shelf-like portion of lower shielding 216which extends between upper lateral casing 218 and lower lateral casing224. In one embodiment, upper lateral casing 218, lower lateral casing224, upper shelf casing 230, and lower shelf casing 232 may beapproximately ⅛ in. thick.

According to a further embodiment, to provide shielding at the topportion of ion exchange vessel 150, such as with respect to riser 158,lead shot may be used. For example, upper chamber 164 in riser 158 maybe filled with lead shot (indicated by arrow 234 in FIG. 12). Asdiscussed below, this method of shielding allows air to flow upward frominner shell 194, through aperture 155 and plate cover 170, and throughaperture 166 and plate cover 168. Further, inspection ports 184, 186formed by tubing 180, 182 may also be filled with lead shot (indicatedby arrow 236 in FIG. 12). A suitable cover, grating, mesh, or the likemay be provided over apertures 176, 178 in middle plate 154 to supportthe lead shot in tubing 180, 182.

As explained above, because the ion exchange process generates largeamounts of heat, it is important to ensure not just that ion exchangevessels are constructed to operate under sufficiently high temperatures,but also that sufficient cooling is provided. This may be particularlytrue with ion exchange using CST media for removal of Cs from liquidsalt wastes, but it is also true with respect to other ion exchangemedia. Moreover, the high temperatures generated during ion exchange maybe much higher along the centerline of the ion exchange vessel, acondition known as “excessive centerline temperature.” In this regard,and as discussed below, embodiments of ion exchange vessel 150 maypreferably comprise a cooling core that displaces or removes the centerion exchange media and facilitates convective air cooling. Notably,thermal analysis of an embodiment of ion exchange vessel 150 without thecooling core demonstrated that, in the absence of active cooling, ionexchange using CST media may generate centerline temperatures of over1000° F. This temperature may increase during storage. By effectivelyremoving the center of ion exchange vessel 150 and providing a coolingcore, however, a hot spot may be eliminated. Moreover, convective airflow is facilitated such that the temperature of embodiments of ionexchange vessel 150 is much lower during both operation and storage.

The cooling core of one embodiment of ion exchange vessel 150 preferablyenables convective air flow along a path through base 160, through avent shield stack 238, through inner shell 194, through aperture 155 andplate cover 170, through upper chamber 164, and ultimately exiting ionexchange vessel 150 through aperture 166 and plate cover 168. In thisregard, base 160 preferably comprises at least one inlet 240 for air topass through base 160. Inlet 240 may preferably comprise a horizontalpassage extending from the outer peripheral surface of base 160 towardvent shield stack 238. In one embodiment, inlet 240 may terminatebeneath vent shield stack 238, but in other embodiments inlet 240 mayextend diametrically across base 160. In yet other embodiments, morethan one inlet 240 may be provided. As shown in FIG. 13, for example,the illustrated embodiment of ion exchange vessel 150 may comprise twoinlets 240.

In a preferred embodiment, base 160 may comprise a plurality of metalplates. As illustrated, for example, base 160 may comprise six plates242, 244, 246, 248, 250, and 252. Plates 242-52 may be arranged in aconcentric, stacked formation and suitably fixed to one another (e.g.,by welding) to provide a cylindrical support structure for ion exchangevessel 150. In one embodiment, base 160 may be approximately 10 in. tallwhen plates 242-52 are stacked together.

More particularly, plate 242 may preferably be circular in shape andformed of carbon steel. In one embodiment, plate 242 may beapproximately 2 in. thick. Plates 246-52 may also be circular in shapeand formed of carbon steel. In one embodiment, plates 246-50 may each beapproximately 2 in. thick, whereas plate 252 may be approximately 1 in.thick. However, those of skill in the art may select suitable dimensionsfor the plates which comprise base 160 based on needed or desiredsupport and shielding for ion exchange vessel 150.

Unlike plate 242, plates 246-52 may preferably each define a centralaperture, which in one embodiment may be circular in shape. It ispreferred that the central apertures of plates 246-52 have the samediameter, which may be substantially equal to the inner diameter ofinner shell 194. Thus, when plates 246-52 are stacked together, thecentral apertures form a hole 254 over plate 244. The depth of hole 254may be defined by the thickness of plates 246-52.

In a preferred embodiment, plates 242 and 246-52 may have an outerdiameter that is substantially equal. For example, the outer diameter ofthese plates may be approximately 55 in. In any event, the outerdiameter of plates 242 and 246-52 is preferably greater than that oflower shielding 216. As explained above, this may further contribute tothe stability, ease of transport, and lower center of gravity of ionexchange vessel 150.

However, as shown in FIGS. 11 & 15, plate 244 may preferably have anouter diameter that is slightly smaller than the outer diameter ofplates 242 and 246-52. In one embodiment, for example, the outerdiameter of plate 244 may be approximately 53 in. Accordingly, whenplates 242-52 are stacked together, base 160 may define a peripheralgroove 256. Air may enter the cooling core of ion exchange vessel 150 atgroove 256, and thus in one embodiment a screen 258 may be affixed overgroove 256, for example to prevent the entry of insects, debris, or thelike. Screen 258, which may be annular in shape and extend around theperiphery of base 160, may be formed of 5 mesh stainless steel, forexample.

In the illustrated embodiment, inlet 240 in base 160 may be defined byplates 242, 244, and 246. More specifically, as shown in FIG. 15, plate244 may be substantially circular in shape but may have at least oneslot 260 defined therethrough. In one embodiment, slot 260 may begenerally rectangular in shape, with a semicircular distal end 262,though slot 260 may take any suitable shape in other embodiments. Forexample, it will be appreciated that the width of slot 260 may varydepending on the amount of air flow needed or desired through inlet 240.Slot 260 may preferably extend radially from the peripheral edge ofplate 244, terminating short of the center of plate 244. In this regard,the length of slot 260 is preferably defined such that slot 260terminates in a position which will be beneath hole 254 defined byplates 246-52.

Here, two slots 260 are defined in plate 244, such that plate 244 maycomprise a first half 264 and a second half 266 connected by arectangular portion 268. In other embodiments, however, a single slot260 or more than two slots 260 may be provided. In any event, becauseslots 260 extend through the thickness of plate 244, when plates 242,244, and 246 are stacked together, inlets 240 are defined.

It will be appreciated that constructing base 160 out of a plurality ofmetal plates may facilitate manufacture of base 160. Still, in otherembodiments, base 160 may comprise fewer than or more than six plates.Indeed, it is contemplated that base 160 may comprise a single, metalplate that is circular in shape and has at least one inlet 240 definedtherein.

After air enters base 160 through one or more inlets 240, it mayencounter vent shield stack 238, as noted above. In one embodiment, ventshield stack 238 may comprise a single metal cylinder having an airpassage defined therethrough. In a preferred embodiment, however, and aswith base 160, vent shield stack 238 may comprise a plurality of platesarranged in a concentric, stacked formation. As shown, vent shield stack238 may comprise 11 such plates, though fewer or more than this numberof plates may be provided in other embodiments. The plates of ventshield stack 238 are preferably formed of carbon steel and may each beapproximately 1 in. think in one embodiment. Further, the plates of ventshield stack 238 may be circular in shape, be substantially equal indimension, and have diameters which are slightly less than the innerdiameter of inner shell 194. Thus, the plates of vent shield stack 238may form a cylindrical structure which may be received in hole 254 (overplate 244) and which may extend upward into inner shell 194.

To allow air entering inlet(s) 240 to pass upward into inner shell 194,at least one radial slot 270 may be defined in each of the plates ofvent shield stack 238. As shown in FIGS. 9 and 11-14, slots 270 may beangularly offset in one embodiment, though this is not required. Forexample, the plates of vent shield stack 238 may preferably be stackedsuch that slots 270 are angularly offset but at least partially overlap.Thus, air may flow upward between the plates of vent shield stack 238 ina stair-step fashion from one plate to the next. Accordingly, ventshield stack 238 may provide additional shielding beneath inner shell194 while still allowing air entering inlet(s) 240 to pass through eachplate of vent shield stack 238 and into inner shell 194.

Finally, one embodiment of ion exchange vessel 150 may have thefollowing approximate specifications. The overall height of the vesselmay be approximately 143 in., and its outer diameter may beapproximately 55 in. The ion exchange media cavity height may beapproximately 108 in., and the ion exchange media bed height may beapproximately 96 in. The ion exchange media cavity volume may beapproximately 100,000 in³, and the volume of loaded ion exchange mediamay be approximately 2 to 5% less than the media cavity volume. Theupper shielding 214 may be approximately 5.44 in. thick, whereas thelower shielding 216 may be approximately 6.94 in. thick. Also, the emptyweight of the vessel (excluding the ion exchange media and lead shot)may be approximately 51688 lbs. The maximum operating weight of thevessel may be approximately 61717 lbs (60502 lbs excluding water).Further, the design operating pressure of the vessel may beapproximately 1.37 MPa (199 PSIG). The design operating temperature ofthe vessel may be 66° C. (150.8° F.).

Embodiments of the present invention provide a process and method fortreatment of radioactive liquid having high levels of certainradionuclides. While one or more preferred embodiments of the inventionhave been described above, it should be understood that any and allequivalent realizations of the present invention are included within thescope and spirit thereof. The embodiments depicted are presented by wayof example only and are not intended as limitations upon the presentinvention. Thus, it should be understood by those of ordinary skill inthis art that the present invention is not limited to these embodimentssince modifications can be made. Therefore, it is contemplated that anyand all such embodiments are included in the present invention as mayfall within the scope and spirit thereof.

What is claimed is:
 1. A vessel for removing radionuclides from a liquidthat flows through the vessel, said vessel being constructed as apressure vessel comprising: a shielded housing comprising an outer shelland an inner shell disposed within said outer shell, said housingdefining an ion exchange chamber between said inner and outer shells,said housing having a shielding that inhibits escape of radiation fromthe ion exchange chamber; an inlet diffuser located inside said ionexchange chamber; an outlet collection structure located inside said ionexchange chamber; a base supporting said housing; a process inlet influid communication with said inlet diffuser; a process outlet in fluidcommunication with said outlet collection structure; and a first fluidpassage extending between an exterior of said vessel and said innershell and a second fluid passage extending between the exterior of saidvessel and said inner shell, wherein said vessel permits convective airflow between said first fluid passage, said inner shell, and said secondfluid passage.
 2. The vessel of claim 1, wherein said inlet diffuser islocated proximate a bottom of said ion exchange chamber and said outletcollection structure is located proximate a top of said ion exchangechamber.
 3. The vessel of claim 1, wherein said housing furthercomprises a riser defining an upper chamber therein.
 4. The vessel ofclaim 3, wherein said upper chamber is filled with lead shot.
 5. Thevessel of claim 1, wherein said housing is shielded by a plurality oflead sheets wrapped around an outer surface of said housing.
 6. Thevessel of claim 1, wherein said first fluid passage extends through saidbase.
 7. The vessel of claim 6, said base comprising a plurality ofstacked base plates arranged horizontally, wherein at least one of saidstacked base plates is a slotted base plate defining at least one slotforming part of the first fluid passage.
 8. The vessel of claim 7,further comprising a vent shield stack disposed along said first fluidpassage.
 9. The vessel of claim 7, wherein at least one of said stackedbase plates defines a central aperture axially aligned with an interiorof said inner shell.
 10. The vessel of claim 9, wherein multiple of saidstacked base plates each define a respective said central aperture whichcollectively define a base hole axially aligned with an interior of saidinner shell.
 11. The vessel of claim 10, further comprising a ventshield stack disposed along said first fluid passage, said vent shieldstack comprising a plurality of stacked vent shield plates located insaid base hole.
 12. The vessel of claim 11, wherein said vent shieldplates define respective radial slots forming part of said first fluidpassage.
 13. The vessel of claim 12, wherein said radial slots ofrespective ones of said vent shield stacks are angularly offset butpartially overlap.
 14. The vessel of claim 7, wherein said slotted baseplate is positioned on top of an imperforate bottom plate and anotherone of the plurality of base plates is positioned on top of said slottedbase plate.
 15. The vessel of claim 14, wherein said slotted base platehas a plurality of slots that form part of the first fluid passage. 16.The vessel of claim 15, wherein said slotted plate has a diameter lessthan that of the bottom plate and the another one of the plurality ofbase plates to define an annular groove around the base.